The Site is a coral atoll comprising 221 hectares of land, including an enclosed central lagoon, and 2,380 hectares of surrounding coral reef and ocean. The atoll is the only largely undisturbed island in the Cocos (Keeling) Islands group that retains its original ecosystems and their species. When first listed, the lagoon had a narrow connection to the Indian Ocean, but natural processes have since closed this. The largely undisturbed nature of the Site facilitates research on the natural distribution of oceanic island species and atoll formation. It is significant for the number of seabirds it supports, including large breeding colonies of red-footed booby (Sula sula) and lesser frigatebirds (Fregata ariel). There is also an endemic resident subspecies of buff-banded rail (Hypotaenidia philippensis). The Site supports plant and animal species that are no longer found on the more southerly islands, including the coconut crab (Birgus latro). Around 200 species of fish have been recorded, with evidence of hybridization of some Indian and Pacific Ocean species which are at the edge of their respective distributions.